1. Field of the Invention
This invention relates to a method and an apparatus for eliminating the high-energy ion that is ejected simultaneously with extremely ultraviolet light (hereinafter abbreviated as xe2x80x9cEUV lightxe2x80x9d) from an EUV light-radiating.
2. Description of the Prior Art
The plasma light source has outstanding characteristics, such as small size, high brilliance, high repetitional operation and ability to radiate short wavelengths emission even reaching the hard X ray. However, the high-energy ion is inevitably emitted simultaneously with the EUV light from the plasma light source and the vicinity thereof in consequence of the formation of plasma, and the maximum speed thereof reaches 106 to 107 cm/s. The high-energy ion inflicts fracture and injury on a multilayer mirror as by spattering and ion implantation and consequently induces it to suffer from deterioration of performance. Further, in the case of an analytical device using EUV light, the admission of this ion possibly results in varying the composition of a given specimen during the operation of the device.
For the purpose of eliminating this high-energy ion, methods directed toward allaying this ion by the collision thereof against an object, such as a gas or a filter, have been heretofore proposed. In the xe2x80x9cX-ray generating apparatusxe2x80x9d disclosed in JP-A HEI 09-320792, for example, scattered particles including the high-energy ion are caused to collide against a gas that has a low X-ray (EUV) absorption factor, thereby eliminating the dispersed particles. Since the gas used for the elimination herein is interposed between the light source and an object for irradiation with the EUV light, the intensity of radiation used in the apparatus is lowered because the gas inevitably absorbs the EUV light as well. A method that contemplates shuttering the high-energy ion by spouting the gas at a high speed in the form of a jet has been proposed. This shutter, however, is incapable of acquiring such a high speed as suffices the expected function because the ratio of expansion of the ion emitted from the plasma differs by more than several decimal places from that of the gas.
As means to eliminate the high-energy ion in the EUV light source, the method which consists in interposing a gas or a filter having a low EUV light absorption factor between the EUV light source and the optical system operating with EUV light has been known to the art as described above. Though this method indeed accomplishes the elimination of the ion as expected, it is fated to entail additional absorption of the EUV light. For the purpose of increasing the quantity of this ion to be eliminated, the object against which the ion is made to collide is required to have the thickness thereof increased and assume a state of high compaction and is consequently suffered to entail an addition to the absorption of EUV light and a remarkable decline in the intensity of EUV light.
None of the known methods which have invariably relied on the collision of the high-energy ion against an object, such as a gas or a filter, to effect the elimination of high-energy ion is capable of effectively eliminating the ion exclusively with no sacrifice of the performance of the EUV light.
This invention has for an object thereof the provision of a method and an apparatus for the elimination of the ion in an EUV light-radiating device, which are capable of effectively eliminating the high-energy ion exclusively without a sacrifice of the intensity of the EUV light.
The method contemplated by this invention for the elimination of a high-energy ion in an EUV light-radiating device comprises irradiating a target with an exciting laser to form a laser-produced plasma EUV light source and causing a high-energy ion generated simultaneously with EUV light to collide against plasma formed by irradiating another target with another laser to separate the high-energy ion exclusively from an orbit of the EUV light.
The apparatus contemplated by this invention for the elimination of a high energy ion in an EUV light-radiating device comprises means for irradiating a target with an exciting laser to form a plasma EUV light source and induce emission of EUV light from the EUV light source, means for irradiating another target with another laser to form plasma for ion elimination, and means for causing a high-energy ion generated simultaneously with the EUV light to collide against the plasma for ion elimination to separate the high-energy ion exclusively from an orbit of the EUV light. For this reason, the plasma for ion elimination has to be formed, with the difference between ion flight time and plasma expansion delayed.
The plasma EUV light source is laser-produced plasma, pinch plasma, or discharge plasma entrapped in a capillary tube. The plasma for the elimination of the high-energy ion embraces plasma that is intended for the formation of a laser.
The collision of the high-energy ion from the EUV light source against the plasma for ion elimination embraces a process of initially allowing passage of the EUV light and subsequently causing the high-energy ion entrained consequently by the EUV light to collide against the plasma.
The target for the formation of the laser-produced plasma EUV light source is formed of B, C, Al, Cu, Xe or Sn, or a compound using any one of the elements as a principal component. The target for the formation of the plasma for the elimination of the ion is formed of Si, Ar, Zn, Ga, Kr, Mo, In, Sn, Xe, Pb or Hg, or a compound using any one of the elements as a principal component.
The laser that forms plasma for ion elimination embraces forming column of plasma for ion elimination by focusing the laser at discrete column on a target or for forming planar plasma for ion elimination by focusing the laser linearly on a target. Plasma expansion forms column shape in the case of spot focusing. Planar plasma is also defined by the linearly longitudinal direction and the plasma blow-off direction. Plasma for ion elimination disposed so that the high-energy ion collides between the light source and the EUV-irradiated medium or EUV mirror.
The surface of the target to be irradiated with the laser to produce the plasma for ion elimination embraces inclining the surface at a predetermined angle so as to prevent the ejected particles issuing from the plasma from impinging at a solid angle on the object irradiated with the EUV light.
It further embraces interposing a plate between the plasma for ion elimination and the object irradiated with the EUV light so as to prevent the ion originating in the plasma from impinging at a solid angle on the object irradiated with the EUV light.
According to this invention, it is made possible by causing the high-energy ion emitted from a plasma EUV light source simultaneously with EUV light to collide against plasma produced by another laser to realize a high-speed shutter with absolutely no loss of the intensity of the EUV light. It is made possible as well by utilizing the collision for separating the orbit of the high-energy ion from the EUV light to materialize long-time exposure to the EUV light without entailing any change of composition by the high-energy ion in a minute specimen used for the irradiation with the EUV light. Since the speed of the low-energy ions and microparticles from EUV light is slow, scattered particles other than the high-energy ion can also be eliminated when using a mechanical shutter in combination with the high-speed shutter.
Furthermore, by combining this invention with partition walls so constructed as to preclude diminution of the solid angle from the EUV light source, it is made possible to effect the elimination of the high-energy ion from the plasma EUV light source even during the collection of the EUV light at a large solid angle.
The other objects and characteristics of this invention will become apparent more specifically from the following description based on the accompanying drawing.